1. Field of the Invention
The present invention relates to a technique for controlling pumping applications; and more particularly, the present invention relates to a method and apparatus for determining instant pump differential pressure and flow rate, and for controlling the pumping applications based upon the determination.
2. Brief Description of Related Art
In previous works by one or more of the inventors of the instant patent application, for hydronic pumping system sensorless control and monitoring, several discrete or numerical sensorless conversion techniques or means were developed and form part of a family of related works set forth in patent documents set forth below, e.g., including that set forth and referenced as documents [3] through [6] below.
For example, following a so-called 3D numerical conversion in the patent document referenced as [3] below, based upon using 3 distribution matrices of pump pressure, flow rate and power with respect to motor speed and system characteristics coefficients, the system pressure and flow rate were converted from a pair of motor readout values directly. The conversion accuracy was reasonably satisfactory, e.g., with around 5% error in the pump normal operation hydronic region.
However, in order to avoid tedious calibration data acquisition when using the 3D conversion method in pumping sensorless control application in field, a mixed discrete and theoretical conversion technique or means was developed and is set forth as well in the patent document referenced as [4] below, e.g., based upon using pump curve and system equations, yielding around 5-8% of the conversion error without the need for instrumentation calibration.
Further, a best-fit affinity sensorless conversion technique was also developed as set forth in patent document referenced as [6] below, e.g., based upon using pump and system characteristics equations together with the empirical power equation. The pump characteristics equation and the empirical power equation are reconstructed by using a polynomial best-fit approach from pump data published by pump manufacturers. System pressures and flow rate were resolved at the steady state equilibrium point of pump and system pressures by using those system and power characteristics equations accordingly, with around a 5% conversion error. However, for slightly more complicated pump pressure and power characteristic distribution curves, it was determined that this technique may pose a slight challenge in order to provide a better representation of the curves and to inverse or resolve those curve equations. The conversion accuracy may not always be satisfactory as well, e.g. for slightly more complicated pump characteristics distributions.
In view of the aforementioned, there remains a need in the pump industry for a better way to determine pump pressure differential and flow rate for sensorless pumping control applications without the need to reconstruct and solve any pump and system characteristics equations.